Prognose: What We Know, What We Don’t Know and What You Should Do

It’s that time again! The 2021/22 Nassau County property tax grievance season is upon us. Get started here. With that bit of housekeeping out of the way, let’s move on to our topic of the month…

Prognose is the software program used by the Nassau County Department of Assessment (DOA) to compute the property values of Class 1 (residential) properties for the 2020/21 tax year.  Purchased in 2018 from software vendor Thimgan & Associates, Prognose came online in November 2018 and currently powers both the internal assessment models used by the DOA and the results displayed on its official public-facing website,

Prognose was licensed to replace an older program called ADAPT that had been used by prior administrations. According to documents filed pursuant to the software purchase, Prognose is superior to the older software in several important respects, including its ability to:

  1. Display comparable property sales on a case-by-case basis.
  2. Access historical modeling data used to establish current baselines.
  3. Generate comprehensible reports so that property owners can easily review the variables and adjustments used to assess their properties.

These new features will help the DOA to demonstrate the methodology used to determine homeowners’ Fair Market Values. If you want to see Prognose in action, go to the County’s site and look up your own property. While you’ll only be able to see the results of a query – not the variables and programming logic powering these results – it’s useful to familiarize yourself with Prognose’s various reports, because they reflect the data the County has compiled on your property.

What We Don’t (Yet) Know

OK; so that’s what we know. But there’s still a lot the public likely doesn’t know about Prognose. Here are some questions worth asking as we go into the 2021/22 Tax Season:

Are the different modifying factors in the 7 Nassau County “markets” used by Prognose fair and equitable?

In August, a Great Neck resident was able to review the actual computer source code released by the County pursuant to a FOIA request. He discovered that the factors used to determine whether a given property improvement results in an increased or decreased tax liability vary widely across Nassau County. In fact, seven different subprograms are used by Prognose to reflect seven different real estate “markets” in Nassau County.

The odd and somewhat troubling consequence of such an arrangement is that the same improvement can receive inconsistent valuations in different markets.  For example, a homeowner in one market who improves his/her property by installing an HVAC system, may have his/her property value increase, whereas a homeowner in a different Nassau County “market” may see no increase in valuation. Similarly, a homeowner with a “Contemporary” style house in one market may see an increase in valuation, whereas the same “Contemporary” style house located in a different “market” will have its value discounted.

While a representative of the County has defended these differing factors by noting that “different market influences move in different ways and have different impacts on value,” it’s still far from clear how exactly the County decided on these factors, or whether they’re truly equitable in each and every case.

Where are the 14 missing data files?

When the County released Prognose’s source code, 14 files (two from each of the seven individual Nassau County “markets”) were omitted. It would aid public understanding if every data file referenced in the source code had been released. Hopefully this omission will be corrected in the near future.

What You Should Do

Do the program’s outputs fairly reflect the value of your own property?

This question is key, and it’s up to you (or us, if you decide to hire us) to find a satisfactory answer.

It’s incumbent upon every Nassau County taxpayer to scrutinize the data compiled by the County in order to evaluate its accuracy. Are the “comparable properties” used in Prognose’s reports actually comparable? Is your home’s actual graded quality reflected accurately? Is the traffic on your local street really “light” or is it “heavy?” Because these and other data points are used by Prognose to compute your property tax liability, it’s vital that they be error-free.

While the County attempts to ensure the accuracy of this underlying data, in reality it lacks the work force to send individual inspectors around to every home to ensure 100 percent accuracy. And you – as a Nassau County taxpayer – have every right to question the data held by the County if you believe that your assessment is wrong.

Yes, you can do all this work on your own, but prudent Nassau County taxpayers know that hiring a firm that specializes in performing this kind of detailed analysis often yields the greatest tax savings. So, we encourage you to sign up with Maidenbaum. We’ll do everything we can to make sure that you never have to shoulder more than your fair share of Nassau County’s property tax burden. Just click here to get started.